Whats the best way for the "DIY" (me) to remove undercoating like ZIEBART or any other under body protection. Now also this is on a 1979. so its been their for awhile.

eastwood company has a product called underoff for removing undercoating ,you might also check your local auto paint supplier for similar products

A heat gun and putty knife for the worst of it.
Easy Off oven cleaner works as well but it's kinda nasty stuff.